Application of Polymeric Super Electrical Insulating Materials to Superconducting Power Apparatus

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The investigators have been studying the application of polymeric materials (ethylene-propylene rubber (EPR)) to electrical insulation system of superconducting power apparatus. The superconducting power apparatus is the promising ways for handling huge electric power efficiently in the future. It is necessary to study the behavior of electrical insulation at cryogenic temperature to evaluate long term reliability as a superconducting apparatus. At cryogenic temperature, there are many practical insulation studies on fluids such as liquid nitrogen or liquid helium but scarce studies on the solid insulation enabling a high voltage design.The results are summarized as follows :(1) The treeing phenomena of EPR insulation at cryogenic temperature have been studied. DC short-circuit treeing tests are performs. DC short-circuit tree initiation voltage at cryogenic temperatures in much higher than that at room temperatures. This may be attributed to loss carrier injection from electrode and gives a strong incentive to design the electrical insulation of superconducting power apparatus.(2) The effect of additives such as crosslinking agent and fillers on tandelta, dielectric dissipation factor of EPR have been measured at cryogenic temperature. The results show that additives increase tandelta of relatively thin films of EPR even in cryogenic temperature region.(3) To design the electrical insulation for a superconducting power apparatus the DC.breakdown voltage of cryogenic gas with and without spacer have been measured. The breakdown voltageobeys Paschen''s law and change only with the product of density and thickness. In low density-thickness product range surface breakdown can hardly occur before the gap breakdown develops.The results obtained in this study open an avenue to the application of polymeric materials (EPR) to electrical insulation system of superconducting power apparatus. EPR seem to be promising materials for solid insulation in the cryogenic region.